to represent the rushing of the swarms of locusts which afflicted the Nile country as the seventh plague, by a principal viola.
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| Fig. 3.—Cicada. |
Several other species of insects have apparatus for producing sounds similar to that of the grasshopper, or modifications of it. Of a different type is that with which the cicadas (Fig. 3) are endowed—the only creatures of this class which have vocal apparatus analogous to those of the higher animals. Only the males of this family are singers, for which the Greek poets called them happy because their females were dumb. With the ancients, a cicada sitting on a harp was the symbol of music. A pretty fable tells of the contest between two cithara-players, in which the curious event happened that when one of the contestants broke a string, a singing cicada sprang on his harp and helped him out so that he gained the prize. The Greeks, who shut the insects in cages so as to be sung to by them in their sleep, were at odds concerning the nature of their singing apparatus; and the controversy among naturalists on the subject lasted till 
Fig. 4.—Tone Apparatus of the Cicada (magnified thirty times). very recently. The zoölogist H. Landois, who investigated the difficult subject of animal sounds with ceaseless industry and great skill, was able to give a satisfactory solution to the question. According to his research, the case is one in which the sound is really made by air circulating through passages in the interior of the body. Every insect's body is penetrated by a system of breathing-tubes or tracheae which open at places on the surface. The openings are called stigmata. This system of breathing-tubes, through which the air is inspired and expired, takes the place of the lung of the higher animals. Landois discovered them in very obscure parts of the cicada, and found that they form a kind of windpipe representing the actual tone-factory of the animals. This air cavity is, as the picture (Fig. 4) shows, not quite open, but has only a narrow cleft (sp), through which the air goes in and out. The cleft is formed by two stretched membranes (sa and sb), which vibrate when the air passes through. They serve, in fact, a like function with the vocal cords of our larynx. They lie, besides, opposite a large cavity over which a folded membrane is stretched like a drum-head upon a hard
